Electronic thermometer with multi range measurement capability

Abstract

The thermometer includes an oscillation unit having a time constant circuit with a compound resistor including a reference resistor and a temperature sensitive resistor. The compound resistor is switched between the reference and temperature sensitive resistors. A comparator compares the oscillation frequencies of the oscillation unit by switching over the compound resistor between the reference and temperature sensitive resistors at a variable sampling interval, and outputs digital data corresponding to the temperature sensed by the temperature sensitive resistor. The digital data corresponding to the sensed temperature are converted and displayed on a temperature data display unit. The resistive value of the reference resistor and the sampling time are switchable according to the range of temperature measurement. The temperature data conversion unit has several sections which are switchably selected according to particular ranges of temperature measurement. Each of these temperature data sections, upon receipt of the digital data from the comparison unit, outputs appropriate temperature data according thereto. A switching unit switches between the various sections of the temperature data conversion unit. A switching control device, in response to the output of the temperature data conversion unit, determines the range of temperature measurement, and appropriately controls the switching actions of the reference resistor, the sampling time switching unit, and the temperature data conversion means switching unit.

What is claimed is: 
     
       1. An electronic thermometer, comprising: (a) an oscillation unit comprising: a time constant circuit comprising:   (i) a resistor device comprising a reference resistor means having selectable plural discrete resistance values and a temperature sensitive resistor means; and   (ii) a switch-over means for switching over said resistor device between said reference resistor means and said temperature sensitive resistor means;     (b) a sampling time switching means cooperating with said switch-over means to periodically switch over said resistor device between said reference resistor means and said temperature sensitive resistor means at one of plural selectable predetermined sampling intervals, in accordance with a selected range of temperature measurement;   (c) a comparison means for comparing oscillation frequencies of said oscillation unit, said comparison means comprising means for outputting digital data corresponding to a temperature sensed by said temperature sensitive resistor means;   (d) a temperature data conversion means, receiving said digital data corresponding to said sensed temperature, for converting said digital data to a corresponding temperature data output;   (e) a means for displaying said temperature data output;   (f) means for selectively switching said reference resistor means from one to another of said resistance values according to the selected range of temperature measurement;   (g) said temperature data conversion means comprising a plurality of selectable operating sections which are individually switchably selected according to said selected range of temperature measurement, each of said operating sections outputting, upon receipt therein of said digital data from said comparison means, a temperature data output corresponding thereto;   (h) a temperature data conversion means switching means for switching between said selectable operating sections of said temperature data conversion means; and   (i) a switching control means which, in response to said temperature data output, determines switching of the range of temperature measurement, and controls (i) said means for selectively switching said reference resistor means, (ii) said sampling time switching means, and (iii) said temperature data conversion means switching means.